1. Field of the Invention
The present invention relates to a surface modification method for improving the formability of aluminum, and more particularly to a method for improving the formability of aluminum alloy sheets by locally modifying the surface of the aluminum alloy sheet.
2. Description of the Prior Art
In the near future, aluminum alloy sheets will be used as key materials in eco-friendly lightweight automobiles, including electrical automobiles and hydrogen automobiles, for various parts, including the inner and outer plates of the car bodies. In particular, work-hardening alloy sheets such as 5000 series aluminum sheets are known to be frequently used for automobiles.
Precipitation-hardening aluminum alloy sheets should be formed in a solid solution treatment condition, because it is difficult to ensure sufficient formability at the peak aging condition. For this reason, there is a very high possibility that distortion of the products will occur in an aging treatment process after forming. On the other hand, work-hardening alloys do not require thermal treatment after being formed into products, and thus distortion of the products does not occur and the effect of an additional increase in strength during the product formation process can be obtained.
However, as the shape of products is diversified, the forming conditions for the products also become increasingly severe. For this reason, in order for alloys to be widely applied to automobiles, it is required to further improve the formability of material itself regardless of the strengthening mechanism of the alloys, or to locally improve the formability of parts on which strains and stresses are concentrated during the formation of products.